The Spooky Spookfish

I like optics so this caught my attention. The brownsnout spookfish is now the first vertebrate to use mirrors to focus images in its eyes. You can see the strange looking spookfish appears to have four eyes, but since the two on the left and the two on the right are part of the same structure, biologists consider them two eyes.

Spookfish live at a depth of about 1000 meters where there is very little light. The two eyes pointing upward (the orange spots) use a traditional cornea to focus light much like our eyes (most of the focusing power of our eyes comes from the cornea. The lens is used to fine tune the focus for nearby or far away objects...as you get older the lens loses flexibility which is why you may be able to see far away just fine but need reading glasses). The other part of the eye points downward (the black spots in the image). Light from below is reflected off a mirror like surface in the eyes and onto the retina. The mirror shows not only what is directly below the fish, but out to about 50 degrees in all directions (which is useful for avoiding predators!) There is evidence that the fish can slightly change the shape of the mirror to focus the images much like our lens changes shape to help us focus.

Some animals (like housecats) have a reflective layer called the tapetum to help them see in dim light. The tapetum lies behind the retina and increases the sensitivity to dim light but does not focus the light.

The spookfish has been known for over 100 years. However, a live specimen was never caught until recently. The deep sea is truly one of the final frontiers on Earth with lots of odd treasures waiting to be discovered.

Reprinted with permission from the Half-Astrophysicst Blog.